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Friday, February 26, 2016

I recently read some comments about early (1970's) wheels flexing enough to eject wheel
covers (full hub caps) when radial tires were first used to replace the original bias tires. This is an example of why it is important to
know if your steel wheels are rated (designed) for radial tire use if you have an older RV that came originally with bias tires and are considering changing to radials.

I think this is more likely to be an issue on old "classic" trailers but it is possible that there are some older (60's vintage and earlier) motorhomes that might have originally come with bias tires also, so this info applies.

Excess flexing can result in steel fatigue which can result in wheel failure. A quick search of the internet found a number of examples:

Note the crack between the two red dots. This is early sign of fatigue crack of the wheel disk.

If the wheel is not replaced this type of crack can grow till the wheel comes apart like this:

Here is a trailer wheel with a complete failure of one spoke:

Fatigue can also occur in the flange area of the rim as seen in this example:

As far as I know most cast aluminum wheels made since the 80's are probably OK for use with radial tires but with the extra side loading seen with multi-axle trailers failure of aluminum wheels is possible too.

I found an excellent video that shows the results of these forces at Keystone RV. Watch the section from time 0:46 to 1:07 and note that the tires on one axle bend inboard while the others are forced outward. This puts tremendous strain on both the tire and the wheel and may lead to failure of either or both parts.
This type of failure may occur after the third or fourth set of tires.

A
side note on wheel failure. I have experienced wheel failure on my race
car after about 3,000 miles usage but these were light weight multi 3
piece wheels with cast center and spun flanges that bolted together.
Application on a relatively heavy car (Camaro) resulted in fatigue failure.
Luckily we were doing magnaflux dye penetrantinspection and discovered the cracks when doing off-season re-build and not during a race.

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Monday, February 15, 2016

Having a tire sidewall failure is one thing that can really spoil an RV vacation. What some fail to realize is that there is also the real potential of personal injury if a tire "blows out" when someone is near by.

The Rubber Manufacturers Association has published some guides on the proper way to handle this potential safety issue. I would like to offer part of that information here. My intent is not to scare you but to inform you that working with tires with high inflation levels is not an activity to be taken lightly. There are practices and procedures that need to be considered if or when you are confronted with the need to inflate or re-inflate your tires.

Steel body tires are usually large tires such as 19.5" and 22.5" but some 16" and 17.5" tires also have steel body cord. You should know what is in your tires and this information is molded on the sidewall of all tires. The material - Steel, Nylon or Polyester are used in most tires today. What we are primarily concerned with is the material in the tire sidewall.

Steel body tires can damage their body cord, no matter how low a speed, if the tire sidewall is over-flexed. Over flexing can occur because of over-load or under-inflation or a combination of the two conditions.

According to the RMA "Permanent damage due to operating a tire underinflated and/or overloaded cannot always be detected. Any tire known or suspected of being operated at 80 percent or less of normal operating inflation pressure and/or overloaded could possibly have permanent sidewall structural damage (steel cord fatigue). Ply cords weakened by underinflation and/or overloading may break one after another, until a rupture occurs in the upper sidewall with accompanying instantaneous air loss and explosive force. This can result in serious injury or death."

In other words, if your normal inflation is 100 psi but you discover you have a tire with 80 psi or less you should NOT re-inflate the tire yourself. If you discover a tire has lost 20% or more of its pressure while being operated you should step away from the tire and contact a service company. All the air should be let out of the tire by removing the valve core.

There are a number of steps that need to be followed. A Safety Inflation cage like this

is also required. The tire is inflated in steps, with the valve core removed.

I know that many people have posted questions on various RV forums asking about what compressor to use to air up their tires, but I am concerned that few realize the potential danger of inflating a tire that has been damaged. Even with 40 years' experience of inspecting tires I cannot be 100% certain the tire has not been damaged.

The best thing to do if you have any question is to have the tire demounted and inspected by a qualified technician at a tire store that sells the type and size tire you have. Not every tire store has the proper safety cage to inflate high pressure tires.

IMO, having a TPMS is one of the best ways for the RV owner to know if a tire is losing air so the RV can be stopped before the tire has lost significant air pressure and is still driven on.

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newsletters about RVing. Great information and advice. Now in our 15th
year. Learn more or subscribe.

Monday, February 1, 2016

For many RV owners the contact information for their tires is easy to find, at least if their tire brand is made or sold by one of the 1st or 2nd tier tire companies. More about tire company tires in a moment. But what should you do if you have a tire question and you can't simply stop at your local tire dealer?

Recently I received a question from an RV owner who had suffered a couple of tire failures and the dealer he bought the tires from had retired and closed up shop. In his case a quick Google search and we discovered that a major chain store that has tire and auto service centers across the country carried the brand in question.

I think it is important to remember that in most cases the tire warranty is the responsibility of the tire manufacturer and not the specific tire dealer.

Keystone also does a very good job of covering care of tires in their "owners manual".

Now there may be some exceptions such as a special Road Hazard warranty sold just by the dealership, but when considering the purchase of such a warranty it is important to review the policy and to understand who is backing the warranty.

Modern Tire Dealer ("MTD"), a tire industry trade journal, in their Jan 2015 issue did an excellent job of covering market share. Now in general they split the market into two groups: Consumer tires (Passenger & LT) in one group, and Truck or commercial tires in the other group. So depending on the type of tire you are interested in you might be more interested in one group than the other. The bad news for many RV owners is that ST type tires are such a small portion of the tire market that they are not identified in the groups, but you might see your tire brand name in one or both groups.

Recently saw a post on another blog Tires and Burst Pressure, What causes a "blowout". Now there was nothing really w...

About RogerBefore retiring, Roger Marble spent 40 years in the tire industry, working for a major manufacturer developing tires for applications in North, Central and South America. During his career he worked on many kinds of tires -- heavy truck, passenger, light truck and Indy-car types. If you have a question for Roger, email him at tireman9(at)gmail.com. or click on this icon to subscribe and get a notice as soon as there is a new post. (about once a week).
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